Lipid Nanodiscs Research Articles

Finding inhibitors and new activators for the biliverdin transporter ABCB10.

The absence of the mitochondrial ATP binding cassette (ABC)-transporter ABCB10 in mice is embryonic lethal, with fetuses presenting severe anemia and oxidative damage. Initially, ABCB10 was thought to be a heme transporter, but recent evidence from our group and collaborators suggests instead that ABCB10 transports biliverdin, a heme degradation product with antioxidant properties. Since some ABC transporters are promiscuous, interacting and/or transporting a large variety of drugs, it is important to determine the specificity of ABCB10 for its substrate. Commonly, ABC transporters present a basal ATPase activity that is increased by substrate binding. As expected, the substrate biliverdin significantly increases the basal ATPase activity of the transporter. Now, we are studying the effect of related compounds on the ATPase activity of purified ABCB10 reconstituted in lipid nanodiscs. We have found inhibition with pyrroles closely related to biliverdin, suggesting that specific substrate-protein interactions are required for the biliverdin-induced activation. We have also found additional compounds (pyrroles and porphyrins) that stimulate the ATPase activity of the transporter, although at a lower level than biliverdin does. Competition assays are underway to determine if these compounds bind to a single site or if there is evidence of the coexistence of multiple drug binding sites on the transporter. Finding compounds that can modulate or inhibit the activity of this essential transporter brings additional tools for needed biochemical and structural studies and opens the door for possible therapeutic purposes. Funding: 1R01GM145938-01 to MEZ.

Molecular and functional interaction of single pass ephrin receptor tyrosine kinase, EphA2 in lipid nanodisc using solution NMR.

Eph receptor, the largest subfamily of single pass trans membrane receptor tyrosine kinase family play crucial role as a regulator during embryonic development, cell maturation, and adulthood. EphA2, a member of the Eph family receptor tyrosine kinases (RTK) is a key regulator of tumorigenesis and cancer progression. EphA2 can be activated canonically by ephrin ligand which normally is a repulsive signal OR non-canonical (unliganded EphA2) promoting cell migration in several cancer types. Here we focus to dissect the effects of the sterile α motif (SAM) domain together with the phosphorylation on intracellular region (ICR) interactions as well as the transmembrane construct of EphA2 in solution to understand the signaling mechanism at molecular level. Our study of the ICR shows that the sterile α motif (SAM) domain acts as a regulator impeding kinase domains interaction and conversely increasing the kinase activity upon deletion of SAM domain. While the presence of the SAM domain hinders oligomerization of phosphorylated ICR, it appears that such protein-protein interactions are required for kinase activity regulation. Mutation studies of the kinase domain, SAM domain and the linker region between kinase domain and SAM domain give insight into its regulatory role for EphA2 activity. More importantly, we have recently optimized truncated construct with single Fibronectin-III, FN-III (Ecto)-Transmembrane (TM)-Juxta-Membrane, JM (ICR) in presence of DDM with well dispersed peaks in TROSY-HQSC indicating well folded protein. We will incorporate this truncated construct into MSP lipid nanodisc for NMR studies and biophysical characterization. In addition to the ICR regulation via SAM domain, we will have in-depth perspective on the configurational coupling of membrane-proximal transmembrane domains to each other.

Structural Insights into Polymer-Bounded Lipid Nanodiscs.

Membrane proteins are an essential part of signaling and transport processes and are targeted by multiple drugs. To isolate and investigate them in their native state, polymer-bounded nanodiscs have become valuable tools. In this study, we investigate the lipid model system dimyristoyl-phosphocholine (DMPC) with the nanodisc-forming copolymers styrene maleic acid (SMA) and diisobutylene maleic acid (DIBMA). Using small-angle X-ray scattering (SAXS) and dynamic light scattering (DLS), we studied the influence of polymer concentration and temperature on the nanodisc structure. In Tris buffer, the size of nanodiscs formed with SMA is smaller compared to DIBMA at the same polymer ratio. In both cases, the size decreases monotonically with increasing polymer concentration, and this effect is more pronounced when using SMA. Measurements at temperatures (T) between 5 and 30 °C in phosphate buffer showed an incomplete solubilization at high T even at polymer/lipid ratios above that required for complete lipid solubilization. For DIBMA, the nanodiscs developed at lower temperatures are stable and the net repulsion increases, while for SMA, the individual nanodiscs possess smaller sizes and are less affected by T. However, using DLS, one can observe SMA agglomerates at low T. Interestingly, for both polymers, no drastic changes of the observable parameters (radius and bilayer thickness) are seen upon cooling, which would indicate a sharp (first-order) phase transition from liquid-crystalline to gel, but only gradual changes. Hence, we conclude that the transition from a gel toward a liquid-crystalline lipid phase proceeds over a broad T-range compared to a continuous lipid bilayer. These results can pave the way toward the development of better protocols for studying membrane proteins stabilized in this type of membrane mimics.

Protein engineering approaches to determine adenosine receptor-G protein interactions.

The adenosine receptor subfamily of G protein-coupled receptors is an important family of membrane receptors that modulate blood pressure and more recently have been implicated in cancer, neurodegenerative diseases, and diabetes, making them a significant fraction of drug discovery efforts. Adenosine A2A receptor (A2AR), one of four subfamily members, has a longer C-terminus than the other adenosine receptor subtypes, which may contribute to its exceptional trafficking to the plasma membrane, but its flexibility has been attributed to protein-protein interactions. Chimeric A1 and A3 receptors with A2AR C-termini showed improved localization to the plasma membrane and are functionally active, with greater than three-fold higher yields than previously reported from other heterologous expression systems. Interestingly, these chimeras are able to bind to their native G proteins, suggesting the specificity of interaction does not rely on the C-terminus. To investigate this further using purified A2AR and Gαs, we determined the affinity and binding rates via surface plasmon resonance (SPR). Together with in vivo signaling data, our results suggest that loss of downstream signaling for the truncation may result from a reduced GPCR-G protein complex interaction, which may be important for interpretation of structure-based drug discovery screening. Current studies are focused on the effect of lipid nanodiscs on A2AR-G protein interactions.

State-specific morphological deformations of the lipid bilayer explain mechanosensitive gating of MSCs ion channels.

The so-called force-from-lipids hypothesis of cellular mechanosensation posits that ion channel gating directly responds to changes in the physical state of the membrane induced for example by lateral tension. Here, we investigate the molecular basis for this transduction mechanism by studying the mechanosensitive ion channel MscS from Escherichia coli and its eukaryotic homolog, MSL1 from Arabidopsis thaliana. First, we use single-particle cryo-EM to determine the structure of a novel open conformation of wild-type MscS, stabilize in thinned lipid nanodisc. Compared with the closed state, the structure shows a reconfiguration of helices TM1, TM2 and TM3a, resulting in widening of the central pore. Based on these structures, we examined how the morphology of the lipid bilayer is altered upon gating, using molecular dynamics simulations. The simulations reveal that, in the absence of extrinsic forces, closed-state MscS causes drastic protrusions in the inner leaflet of the lipid bilayer. These deformations develop to provide adequate solvation to hydrophobic features of the protein surface, and clearly reflect a high energy conformation for the membrane. Strikingly, the protrusions are largely eradicated upon channel opening. An analogous computational study of open and closed states of MSL1 recapitulates these findings. The gating equilibrium of MscS channels thus appears to be dictated by two opposing conformational preferences, namely those of the lipid membrane and of the protein structure. We theorize that membrane tension controls this balance because it increases the energetic cost of the membrane deformations that specifically stabilize the closed channel, shifting the gating equilibrium towards the conductive form.

Direct interactions between picornavirus 3CD protein and phosphoinositide lipids in virus replication organelles.

Positive-strand RNA viruses disrupt host membrane systems and reconstitute these materials into so-called replication organelles, which serve as sites for virus replication and genome packaging. In picornaviruses, these new membrane systems are enriched in phosphoinositide lipids, including phosphoinositide-4-phosphate (PI4P). The 3CD polyprotein is central to membrane biogenesis, as it was previously shown that ectopic expression of 3CD leads to PI4P induction and redistribution, a phenotype similar to that of poliovirus-infected cells. Here, we have shown direct interaction between poliovirus 3CD and PI4P using nuclear magnetic resonance (NMR) spectroscopy, especially providing atomic-level insights into PI4P interaction with both the 3C protease and 3D polymerase derived domains of 3CD. Our studies using paramagnetically-labeled lipid nanodiscs demonstrated that 3C interacts peripherally with the membrane through its positively charged N-terminal helix, which also interacts with genome RNA sequences important for coordinating replication and translation processes. Extension of the C-terminus of 3C increases its affinity to PI4P-containing membranes, suggesting a means by which interactions may change between 3CD and its processed counterparts. Adjustments to virus protein-membrane interactions may be an important component of the switch from replication to packaging modes on these membranes.

Release of nanodiscs from charged nano-droplets in the electrospray ionization revealed by molecular dynamics simulations

Electrospray ionization (ESI) is essential for application of mass spectrometry in biological systems, as it prevents the analyte being split into fragments. However, due to lack of a clear understanding of the mechanism of ESI, the interpretation of mass spectra is often ambiguous. This is a particular challenge for complex biological systems. Here, we focus on systems that include nanodiscs as membrane environment, which are essential for membrane proteins. We performed microsecond atomistic molecular dynamics simulations to study the release of nanodiscs from highly charged nano-droplets into the gas phase, the late stage of ESI. We observed two distinct major scenarios, highlighting the diversity of morphologies of gaseous product ions. Our simulations are in reasonable agreement with experimental results. Our work provides a detailed atomistic view of the ESI process of a heterogeneous system (lipid nanodisc), which may give insights into the interpretation of mass spectra of all lipid-protein systems.

Nanotechnology-enabled immunogenic cell death for improved cancer immunotherapy

Tumor immunotherapy has revolutionized the field of oncology treatments in recent years. As one of the promising strategies of cancer immunotherapy, tumor immunogenic cell death (ICD) has shown significant potential for tumor therapy. Nanoparticles are widely used for drug delivery due to their versatile characteristics, such as stability, slow blood elimination, and tumor-targeting ability. To increase the specificity of ICD inducers and improve the efficiency of ICD induction, functionally specific nanoparticles, such as liposomes, nanostructured lipid carriers, micelles, nanodiscs, biomembrane-coated nanoparticles and inorganic nanoparticles have been widely reported as the vehicles to deliver ICD inducers in vivo. In this review, we summarized the strategies of different nanoparticles for ICD-induced cancer immunotherapy, and systematically discussed their advantages and disadvantages as well as provided feasible strategies for solving these problems. We believe that this review will offer some insights into the design of effective nanoparticulate systems for the therapeutic delivery of ICD inducers, thus, promoting the development of ICD-mediated cancer immunotherapy.

State-specific morphological deformations of the lipid bilayer explain mechanosensitive gating of MscS ion channels.

The force-from-lipids hypothesis of cellular mechanosensation posits that membrane channels open and close in response to changes in the physical state of the lipid bilayer, induced for example by lateral tension. Here, we investigate the molecular basis for this transduction mechanism by studying the mechanosensitive ion channel MscS from Escherichia coli and its eukaryotic homolog MSL1 from Arabidopsis thaliana. First, we use single-particle cryo-electron microscopy to determine the structure of a novel open conformation of wild-type MscS, stabilized in a thinned lipid nanodisc. Compared with the closed state, the structure shows a reconfiguration of helices TM1, TM2, and TM3a, and widening of the central pore. Based on these structures, we examined how the morphology of the membrane is altered upon gating, using molecular dynamics simulations. The simulations reveal that closed-state MscS causes drastic protrusions in the inner leaflet of the lipid bilayer, both in the absence and presence of lateral tension, and for different lipid compositions. These deformations arise to provide adequate solvation to hydrophobic crevices under the TM1-TM2 hairpin, and clearly reflect a high-energy conformation for the membrane, particularly under tension. Strikingly, these protrusions are largely eradicated upon channel opening. An analogous computational study of open and closed MSL1 recapitulates these findings. The gating equilibrium of MscS channels thus appears to be dictated by opposing conformational preferences, namely those of the lipid membrane and of the protein structure. We propose a membrane deformation model of mechanosensation, which posits that tension shifts the gating equilibrium towards the conductive state not because it alters the mode in which channel and lipids interact, but because it increases the energetic cost of the morphological perturbations in the membrane required by the closed state.

Functional reconstitution and structural characterization of the plant hormone receptor ETR1 in lipid nanodiscs.

The plant hormone receptor ETR1 regulates many highly relevant agronomic processes. Today, significant functional and structural questions remain unanswered regarding its multi-pass transmembrane sensor domain able to bind and respond to the gaseous plant hormone ethylene at femtomolar concentrations. A significant reason for this is the lack of structural data on full-length ETR1 in a lipid environment. Herein, we present the functional reconstitution of recombinant full-length ETR1 purified and solubilized from a bacterial host into lipid nanodiscs, allowing the study of the purified plant receptor for the first time in a detergent-free membrane-like environment.

Astrocytic MicroRNAs and Transcription Factors in Alzheimer’s Disease and Therapeutic Interventions

Astrocytes are important for maintaining cholesterol metabolism, glutamate uptake, and neurotransmission. Indeed, inflammatory processes and neurodegeneration contribute to the altered morphology, gene expression, and function of astrocytes. Astrocytes, in collaboration with numerous microRNAs, regulate brain cholesterol levels as well as glutamatergic and inflammatory signaling, all of which contribute to general brain homeostasis. Neural electrical activity, synaptic plasticity processes, learning, and memory are dependent on the astrocyte-neuron crosstalk. Here, we review the involvement of astrocytic microRNAs that potentially regulate cholesterol metabolism, glutamate uptake, and inflammation in Alzheimer's disease (AD). The interaction between astrocytic microRNAs and long non-coding RNA and transcription factors specific to astrocytes also contributes to the pathogenesis of AD. Thus, astrocytic microRNAs arise as a promising target, as AD conditions are a worldwide public health problem. This review examines novel therapeutic strategies to target astrocyte dysfunction in AD, such as lipid nanodiscs, engineered G protein-coupled receptors, extracellular vesicles, and nanoparticles.

Paclitaxel-Loaded Cationic Fluid Lipid Nanodiscs and Liposomes with Brush-Conformation PEG Chains Penetrate Breast Tumors and Trigger Caspase-3 Activation.

Novel approaches are required to address the urgent need to develop lipid-based carriers of paclitaxel (PTX) and other hydrophobic drugs for cancer chemotherapy. Carriers based on cationic liposomes (CLs) with fluid (i.e., chain-melted) membranes (e.g., EndoTAG-1) have shown promise in preclinical and late-stage clinical studies. Recent work found that the addition of a cone-shaped poly(ethylene glycol)-lipid (PEG-lipid) to PTX-loaded CLs (CLsPTX) promotes a transition to sterically stabilized, higher-curvature (smaller) nanoparticles consisting of a mixture of PEGylated CLsPTX and PTX-containing fluid lipid nanodiscs (nanodiscsPTX). These CLsPTX and nanodiscsPTX show significantly improved uptake and cytotoxicity in cultured human cancer cells at PEG coverage in the brush regime (10 mol % PEG-lipid). Here, we studied the PTX loading, in vivo circulation half-life, and biodistribution of systemically administered CLsPTX and nanodiscsPTX and assessed their ability to induce apoptosis in triple-negative breast-cancer-bearing immunocompetent mice. We focused on fluid rather than solid lipid nanodiscs because of the significantly higher solubility of PTX in fluid membranes. At 5 and 10 mol % of a PEG-lipid (PEG5K-lipid, molecular weight of PEG 5000 g/mol), the mixture of PEGylated CLsPTX and nanodiscsPTX was able to incorporate up to 2.5 mol % PTX without crystallization for at least 20 h. Remarkably, compared to preparations containing 2 and 5 mol % PEG5K-lipid (with the PEG chains in the mushroom regime), the particles at 10 mol % (with PEG chains in the brush regime) showed significantly higher blood half-life, tumor penetration, and proapoptotic activity. Our study suggests that increasing the PEG coverage of CL-based drug nanoformulations can improve their pharmacokinetics and therapeutic efficacy.

Nanodisc Lipids Exhibit Singular Behaviors Implying Critical Phenomena.

Nanodiscs are broadly used for characterization of membrane proteins as they are generally assumed to provide a near-native environment. In fact, it is an open question whether the physical properties of lipids in nanodiscs and membrane vesicles of the same lipid composition are identical. Here, we investigate the properties of lipids (1,2-dipalmitoyl-sn-glycero-3-phosphocholine, 1,2-dilauroyl-sn-glycero-3-phosphocholine, and their mixtures) in two different sample types, nanodiscs and multilamellar vesicles, by means of spin-label electron spin resonance techniques. Our results provide a quantitative description of lipid dynamics and ordering, elucidating the molecular details of how lipids in the two sample types behave differently in response to temperature and lipid composition. We show that the properties of lipids are altered in nanodiscs such that the dissimilarity of the fluid and gel lipid phases is reduced, and the first-order phase transitions are largely abolished in nanodiscs. We unveil that the ensemble of lipids in the middle of a nanodisc bilayer, as probed by the end-chain spin-label 16-PC, is promoted to a state close to a miscibility critical point, thereby rendering the phase transitions continuous. Critical phenomena have recently been proposed to explain features of the heterogeneity in native cell membranes. Our results lay the groundwork for how to establish a near-native environment in nanodiscs with simple organization of lipid components.

Corseting a tripartite ABC transporter to make it fit for transport

ABC transporters have long been known to mediate resistance phenotypes in all kingdoms of life, and ATP-driven tripartite efflux pump from Gram-negative bacteria have attracted increasing interest. We give a special focus on MacAB TolC, a prototypical member of the recently described Type VII ABC transporter superfamily, from Escherichia coli. We provide original experimental evidence for the in vitro, substrate-induced ATPase activity and show a maximal activity when the tripartite pump is fully assembled in lipid nanodiscs. These results are evaluated and interpreted in the context of the structural and functional data that have accumulated over the years.

Structure of the GOLD-domain seven-transmembrane helix protein family member TMEM87A.

TMEM87s are eukaryotic transmembrane proteins with two members (TMEM87A and TMEM87B) in humans. TMEM87s have proposed roles in protein transport to and from the Golgi, as mechanosensitive ion channels, and in developmental signaling. TMEM87 disruption has been implicated in cancers and developmental disorders. To better understand TMEM87 structure and function, we determined a cryo-EM structure of human TMEM87A in lipid nanodiscs. TMEM87A consists of a Golgi-dynamics (GOLD) domain atop a membrane-spanning seven-transmembrane helix domain with a large cavity open to solution and the membrane outer leaflet. Structural and functional analyses suggest TMEM87A may not function as an ion channel or G-protein coupled receptor. We find TMEM87A shares its characteristic domain arrangement with seven other proteins in humans; three that had been identified as evolutionary related (TMEM87B, GPR107, and GPR108) and four previously unrecognized homologs (GPR180, TMEM145, TMEM181, and WLS). Among these structurally related GOLD domain seven-transmembrane helix (GOST) proteins, WLS is best characterized as a membrane trafficking and secretion chaperone for lipidated Wnt signaling proteins. We find key structural determinants for WLS function are conserved in TMEM87A. We propose TMEM87A and structurally homologous GOST proteins could serve a common role in trafficking membrane-associated cargo.

How Choice of Model Membrane Affects Protein-Glycosphingolipid Interactions: Insights from Native Mass Spectrometry.

Interactions between glycan-binding proteins (GBPs) and glycosphingolipids (GSLs) are involved in numerous physiological and pathophysiological processes. Many model membrane systems are available for studying GBP-GSL interactions, but a systematic investigation has not been carried out on how the nature of the model membrane affects binding. In this work, we use electrospray ionization mass spectrometry (ESI-MS), both direct and competitive assays, to measure the binding of cholera toxin B subunit homopentamer (CTB5) to GM1 ganglioside in liposomes, bilayer islands [styrene maleic acid lipid particles (SMALPs), nanodiscs (NDs), and picodiscs (PDs)], and micelles. We find that direct ESI-MS analysis of CTB5 binding to GM1 is unreliable due to non-uniform response factors, incomplete extraction of bound GM1 in the gas phase, and nonspecific CTB5-GM1 interactions. Conversely, indirect proxy ligand ESI-MS measurements show that the intrinsic (per binding site) association constants of CTB5 for PDs, NDs, and SMALPs are similar and comparable to the affinity of soluble GM1 pentasaccharide (GM1os). The observed affinity decreases with increasing GM1 content due to molecular crowding stemming from GM1 clustering. Unlike the smaller model membranes, the observed affinity of CTB5 toward GM1 liposomes is ∼10-fold weaker than GM1os and relatively insensitive to the GM1 content. GM1 glycomicelles exhibit the lowest affinity, ∼35-fold weaker than GM1os. Together, the results highlight experimental design considerations for quantitative GBP-GSL binding studies involving multisubunit GBPs and factors to consider when comparing results obtained with different membrane systems. Notably, they suggest that bilayer islands with a low percentage of GSL, wherein clustering is minimized, are ideal for assessing intrinsic strength of GBP-GSL interactions in a membrane environment, while binding to liposomes, which is sub-optimal due to extensive clustering, may be more representative of authentic cellular environments.

Structural Insights into the Mechanism of HIV-1 Tat Secretion from the Plasma Membrane

Human immunodeficiency virus type 1 (HIV-1) trans-activator of transcription (Tat) is a small, intrinsically disordered basic protein that plays diverse roles in the HIV-1 replication cycle, including promotion of efficient viral RNA transcription. Tat is released by infected cells and subsequently absorbed by healthy cells, thereby contributing to HIV-1 pathogenesis including HIV-associated neurocognitive disorder. It has been shown that, in HIV-1-infected primary CD4 T-cells, Tat accumulates at the plasma membrane (PM) for secretion, a mechanism mediated by phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2). However, the structural basis for Tat interaction with the PM and thereby secretion is lacking. Herein, we employed NMR and biophysical methods to characterize Tat86 (86 amino acids) interactions with PI(4,5)P2 and lipid nanodiscs (NDs). Our data revealed that Arg49, Lys50 and Lys51 (RKK motif) constitute the PI(4,5)P2 binding site, that Tat86 interaction with lipid NDs is dependent on PI(4,5)P2 and phosphatidylserine (PS), and that the arginine-rich motif (RRQRRR) preferentially interacts with PS. Furthermore, we show that Trp11, previously implicated in Tat secretion, penetrates deeply in the membrane; substitution of Trp11 severely reduced Tat86 interaction with membranes. Deletion of the entire highly basic region and Trp11 completely abolished Tat86 binding to lipid NDs. Our data support a mechanism by which HIV-1 Tat secretion from the PM is mediated by a tripartite signal consisting of binding of the RKK motif to PI(4,5)P2, arginine-rich motif to PS, and penetration of Trp11 in the membrane. Altogether, these findings provide new insights into the molecular requirements for Tat binding to membranes during secretion.

Structure of SARS-CoV-2 M protein in lipid nanodiscs.

SARS-CoV-2 encodes four structural proteins incorporated into virions, spike (S), envelope (E), nucleocapsid (N), and membrane (M). M plays an essential role in viral assembly by organizing other structural proteins through physical interactions and directing them to sites of viral budding. As the most abundant protein in the viral envelope and a target of patient antibodies, M is a compelling target for vaccines and therapeutics. Still, the structure of M and molecular basis for its role in virion formation are unknown. Here, we present the cryo-EM structure of SARS-CoV-2 M in lipid nanodiscs to 3.5 Å resolution. M forms a 50 kDa homodimer that is structurally related to the SARS-CoV-2 ORF3a viroporin, suggesting a shared ancestral origin. Structural comparisons reveal how intersubunit gaps create a small, enclosed pocket in M and large open cavity in ORF3a, consistent with a structural role and ion channel activity, respectively. M displays a strikingly electropositive cytosolic surface that may be important for interactions with N, S, and viral RNA. Molecular dynamics simulations show a high degree of structural rigidity in a simple lipid bilayer and support a role for M homodimers in scaffolding viral assembly. Together, these results provide insight into roles for M in coronavirus assembly and structure.

Biohybrid Membrane Formation by Directed Insertion of Aquaporin into a Solid-State Nanopore.

Biohybrid nanopores combine the durability of solid-state nanopores with the precise structure and function of biological nanopores. Particular care must be taken to control how biological nanopores adapt to their surroundings once they come into contact with the solid-state nanopores. Two major challenges are to precisely control this adaptability under dynamic conditions and provide predesigned functionalities that can be manipulated for engineering applications. In this work, we report on the computational design of a distinctive class of biohybrid active membrane layers, built from the directed-insertion of an aquaporin-incorporated lipid nanodisc into a model alkyl-functionalized silica pore. We show that in an aqueous environment when a pressure difference exists between the two sides of the solid-state nanopore, the preferential interactions between the hydrocarbon tail of the lipid molecules that surround the aquaporin protein and the alkyl group functionalizing the interior surface of the silica nanopore enable the insertion of the aquaporin-incorporated lipid shell into the nanopore by forcing out the water molecules. The same preferential interactions are responsible for the structural stability of the inserted aquaporin-incorporated lipid shell as well as the water sealing properties of the lipid–alkyl interface. We further show that the aquaporin protein stabilized in the alkyl-functionalized silica nanopore preserves its biological structure and function in both pure and saline water, and, remarkably, its water permeability is equal to the one measured in the biological environment. The designed biohybrid membrane could pave the way for the development of durable transformative devices for water filtration.

Review of Structure of SARS-CoV-2 M protein in lipid nanodiscs

Review of Structure of SARS-CoV-2 M protein in lipid nanodiscs